The objective of this proposal is to develop new information on molecular structures and processes that underlie contraction and relaxation in cardiac and skeletal fast and slow muscles. Efforts will be made to characterize those regions of myosin that are involved in intersubunit, ATP and actin interactions and those that play a role in the sequential motion of myosin (hinge). These motions are crucial to the cross-bridge cycle and the mechano-chemical transduction process in muscle. Components of the system controlling the Ca2 ion dependent interaction of actin and myosin will be further studied with a view to establishing functionally important regions in the troponin subunits. Functionally important residues will be identified and will serve as anchoring points for donors or acceptors in fluorescent energy transfer experiments and for spin labels. Correlations will be sought between physiological processes and biochemical events in cardiac and various types of skeletal muscles. Finally, information on molecular properties of components of the contractile/regulatory system will be used to analyze events in hormone and functionally induced transformations of muscle in cardiac hypertrophy.